Knife grinder &#; plastics shredder and how to choose suitable machine?
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1. What is knife grinder
2. How does knife grinder work
3. What types of grinders exist
4. What objects and materials are processable
5. What are the advantages and disadvantages of grinding technology
6. What are the most common minuses of the grinders
7. What parameters are important for the right choice of suitable grinder
8. Summary
1. What is knife grinder?
Knife grinder is one of many equipments for reducing of object&#;s size, materials, waste and raw materials which we need to be reduced from any reason. We will focus above all on the description of knife grinders for processing of plastics in various forms and with different processing result. These equipments are sometimes incorrectly called as &#;shredders&#;, &#;granulators&#;, sometimes we even meet with the name &#;scrapper&#;, which is from the matter of the construction of course misleading.
2. How does knife grinder work?
Knife grinder for plastics processing has some essential technical characteristics. The base is existence of the flow of processed material into hopper, over grinding chamber of the grinder up to container for processed material. Knife grinder is always equipped with rotating shaft which contains mostly several rotor knives. In the grinding chamber are also stator knives plus the screen with corresponding size. Material goes through the hopper into grinding chamber where is caught by rotor knives and pushed towards stator knives. Adequate part of the material is cut off mechanically. Cutted-off material is cut off again in grinding chamber with rotor knives and grinded into smaller fractions until the material falls through the screen with suitable chosen size. Regrinded material which falls through the screen is collected in the container under the grinding chamber. Material is subsequently transported away from the grinder &#; mostly with the air flow (to another processing or storing).
3. What types of grinders exist?
As already mentioned, knife grinders are not the only type of grinders or equipments for reducing of material size. If we focus on above all our favorite range of plastics processing, real we can take into consideration even follows eguipments:
- guillotine shears &#; for initial pre-portioning of large-volume materials. By means of the pressure of one knife against the other one comes to mechanical pre-portioning of the material.
- shredders (pre-shredders) &#; used mostly for initial pre-portioning of large-volume and masive parts and materials into rough fractions (most often around 20&#;50 mm) which are then suitable for processing into even smaller fractioncs. For further processing are used for example knife granulators. The reason is that shredders are mostly slow-speeded and force oriented machines with rotating shaft (single- or multi-shaft) and their usage for producing of smaller fractions is uneconomic.
- knife grinders &#; economical effective suitable solution for processing of non-bulky and non-masive parts or for processing of larger fractions, for example from shredders. The result is the fraction which is closest to the new processed material (mostly in the granulate form of size cca 4 mm).
- tooth grinders &#; rotor shafts of such grinders are equipped with many same teeth of different shapes. These rotating teeth push processed material towards stator teeth and the material is grinded by cutting into smaller fractions. Tooth grinder are not equipped with the screen, it means the the resulted material fraction is given by the size of individiual teeth.
- hammer mills &#; closest to grinding technology, farthest from cutting technology. The rotor is equipped with pendulous hammers. By rotation of these hammers rises on their ends kinetic energy; by hitting of the hammers to the processed material comes to its pre-portioning into smaller fractions; but this technology is conceivable only by processing of hard and brittle materials and absolutely not suitable for processing of elastic materials.
- disc mills (pulverizers) &#; eventual next stage for processing of fractions around 4 mm into even finer or dusty material, with fraction size cca to 1 mm. Pulverizers use rotation of one of two grinding discs with fine teething. Material goes from the hopper in the middle of stationary disc. The material is by means of centrifugal force pushed to the edges of the discs, where minimal gap is adjusted. Through this gap fine fractions come out from the grinding chamber and the air transports them on fine screen. Rougher fractions (so called above-screen) come back into the grinding chamber for further processing. Fine fractions (under-screen) are collected for futher processing.
Knife granulators for plastics processing (if we skip the processing of municipal plastic waste) are used mostly by initial production of plastic products by injection, extrusion blowing and extrusion technologies. The purpose is to transform NOK products and process waste (for example sprues and cutoffs) back to useful form of input raw material, most often into recyclate with fraction size cca 4 mm, and to use this material for producing of final product again. Let us talk now about technologies and what kind of waste rises from them:
- plastic injection technology &#; here we process various defective multishaped parts and by moulds with cold sprue also sprue groups.
- extrusion blowing &#; we process defective products and oversprues. Depending on given product it can happen that by shape-complicated parts &#; for example air conduction by car dash boards &#; the oversprues can sometimes create even 80 % of material weight from each cycle. So especially this technology is unimaginable without using of knife grinders which are most often integrated directly into in-line process right beside the blowing extruder.
- extrusion &#; production by means of extrusing of endless profile, pipe, sheet, film and so on. Demanding material entrances before stabilizing of the process, shape-unstable edge cutoffs by production of sheets or cast films make large base for reprocessing of such material, ideally on knife granulator again.
When it comes to kind of materials, it makes sense to process on knife granulators for further use only thermoplastics or thermoplastic elastomers. There are many concrete types of materials and it is not the goal of this article to name them all.
Less meaningful is processing of another materials, as silicons, rubbers, thermosets, resins and other types of reactoplastics. Their reusing in the process is nearly impossible, maximally as some type of filler in limited quantity. The purpose of waste processing from these materials could be only reducing of their size for final disposal.
Grinding technology of processed materials enables further handling with this material and its eventual reusing in production process. If we can process mechanicaly regrined recyclate, then we have valuable material which was stressed only mechanically and which is for sure an advantage. Disadvantage is that the individual fractions are not regular. We have certain dust part here, finer and rougher granulates of irregular shapes. We can illustrate this size character with Gauss curve.
Certain disadvantage of material processing on the grinders (any) is level noise and dustiness. However, nowadays are standardly available solutions like sound-proof enclosures and in case of regularly and correct maintenance also dust elimination.
Let&#;s return shortly to the possibility of recyclate processing on thermo-regranulation line. It is the next intercomponent in the logistic of material processing. Recyclate from the grinder is thermally overprocessed, homogenisated and extruded again into tiny formations (lenses, small cylinders etc.) which shapes only minimally differs from original input materials. Their bulky and stable dimension properties are on the higher level than the recyclate from the grinder. On the other hand, disadvantage is another energy, space and financial demandingness and another thermal stressing of processed material. However, for some material types is this execution suitable or even necessary.
Any equipment including knife grinders requiers regular maintenance and checks. Among most common production failures belong lack of maintenance of these equipments, overloading of their capacities and their unsuitable using, eventually wrong choice. We can say in generally that above mentioned failures are caused mostly by persons who work with the grinders.
Maintenance &#; practically almost no one reads the manual or keeps the provisions in it. It concerns mainly the time schedule for check of individual grinder parts, eventually the wrong evaluation of grinder conditions. By knife grinder it is very important to check regularly whether the knives are sharp and screens undamaged. There is one rule &#; he who sharps, then he grinds. There is also another thing &#; I sharp more often while less. In opposite case is the grinder unnecessarily stressed (bearings, shafts), we get recyclate with larger dust part and we reach lower hour rates. The same applies for checking of bearings lubrication (lubricate more often while less), checking of mechanical wearing especially of grinding chamber and repairs on time.
Overloading and unsuitable using &#; the operators change frequently, new operators are not trained enough or not trained at all and many faults happen. Typical is overfilling of the hopper with the material; material stays in the grinder for too long, overheats and the grinding effect is then lower. The similar case is when the operator overdoes the grinder possibilites and tries to grind masive parts. This causes big mechanical swings, or the grinder get stucked and stops. Pushing of the parts in the hopper (for example with wooden sticks) is also incorrect (work safety, contamination of processed material). The material has to fall into grinding chamber on its own, by means of gravitation. It is obvious that before grinding will be removed from the material all impurities, mainly metal parts, which cause significant wearing and damage of the knives and subsequently contaminate material for the next processing. Responsibility and discipline of the operators is absolutelly outright.
Wrong choice &#; it happens that the grinder is purchased for concrete processing of the material; later the production is changed and the grinder is used for another, unsuitable application. I would recommend here to better sell the grinder and buy some more suitable machine.
Let us focus on the right choice of the knife grinder. We have to clarify some questions:
- what do we want to grind &#; what part shape, what will be the smallest and the largest size
- from what kind of material is the considered part and if it suitable to be grinded (see reusing of the material, thermoplastics, thermosets, reactoplastics and so on)
- what is expected material output (fraction size), what is expected hour rate
- what will be the logistic of material flow, will it be filled manually or with the robot or conveyor, if the grinder will be used for in-line recyclation or as a central grinder, how and where will be the final recyclate transported &#; whether to next processing or to storing
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- grinder placement &#; next to other production machines or in separate place, what level of dustiness and noise can be spread into the surroundings
- level of comfort of using of the grinder, what options the customers requires, how is eventual connection of the grinder with another equipments (conveyor belt, metal detector, transport blower, grinder in protective cage right beside the machine etc.)
- if there are any special demands for working place, impact on securing of work safety is always on the first place
- experiences of the customer and the seller with similar applications
- price optimalisation of the solution &#; there are always several various solutions which are either technically or financially on different level. There is no rule that the more expensive equipment means better solution
Knife grinders are essential helpers by processing of technological waste in production. Knife grinders create frame part of grinders, which find their use by processing of plastic materials. They are very often the right solution for whole range of production technologies by which is suitable reprocessing of technological waste. Knife grinders &#; compared with another grinders &#; show advantageous rate price/output and with regular and correct maintenance also low operational costs. Despite these facts we find significant differencies in details of technical solutions of individual grinder producers with direct impact on operating ergonomy, reliability, quickness and simplicity of the cleaning. Very important is also initial communication with the seller so the customer would after all choose optimal solution for purchasing of new grinder. Whether the seller, or the producer would be pleased to share their experiences and to offer their know-how.
What kind of garden shredder do I need?
Find the perfect garden shredder for your needs with these tips and information
For many people, their own green paradise is a source of well-being and tranquillity, as it is the perfect place to recharge their batteries after a stressful day at work. But no pain, no gain: gardens are home to all kinds of plants, shrubs and trees - and as we all know, they need to be looked after. If you don't want to get bogged down in sweaty work, it's definitely worth buying a garden shredder. These practical devices transform branches, twigs, leaves and all other natural garden waste into small shredded material in no time at all, quickly restoring space and order to your home garden.
Unfortunately, the road to your own garden shredder can sometimes be quite bumpy. There are various types of wood chippers that differ fundamentally from one another. You are guaranteed to come across terms such as electric, petrol, blade or drum shredder. Of course, all of these different designs and drive types have their individual advantages and disadvantages, which you should be aware of.
In this guide, we have summarized useful information and helpful tips to help you find the ideal garden shredder for every application. Important points such as work safety and maintenance work are also addressed. So nothing stands in the way of effective shredding in the future. Enjoy reading!
When is a garden shredder a good choice?
More and more people nowadays have a garden shredder as part of their basic equipment, as it guarantees a well-tended garden in which they feel at home. Other names for this garden tool are also common in the trade, such as chipper, wood chipper or simply shredder. No matter what the product is called, the main task is always the same: a garden shredder is used to shred garden waste (branches, twigs, leaves and other organic plant debris) as efficiently as possible.
However, it would be a mistake to think that one garden shredder is like all the others. Just as there are different areas of application, there are also different types of shredders. We would like to present these in more detail in the following sections.
The different types of garden shredders
The market offers a wide variety of garden shredders for different needs, which can be differentiated according to function, energy source and price range:
Primarily, we differentiate between three main modes of operation of garden shredders. Blade shredders are ideal for shredding softer, green plant material, as they use rotating blades to shred the waste. Drum shredders, also known as "silent" shredders, shred garden waste between counter-rotating rollers. They are particularly effective for woody waste and branches. Turbine shredders have a special roller system with a usually conically shaped hopper and can process a wide range of garden waste.
There are basically two types of drive for shredders - they are available with both electric and petrol engines. Electric garden shredders are generally lighter, quieter and easier to operate. They are suitable for smaller gardens or less frequent use. As they rely on a cable, an on-site power source is required, which makes the electric shredder less mobile.
Petrol shredders are naturally more powerful and are better suited to larger gardens and longer work with lots of wood and branches. They are mobile, as they do not require an external power source. Thanks to the powerful motor, they are also suitable for thicker branches and save a lot of time and effort when gardening.
The costs for the different types of garden shredders vary greatly depending on the type and model required. Prices start at around 100 euros for very simple devices, but high-quality shredders can be more expensive.
When choosing the right garden shredder, however, it is most important that you consider your individual needs, e.g. the size of the garden and the type of waste you usually need to process.
Drum shredder
A fairly common variant of the garden shredder is the so-called drum shredder. Typically, the material to be shredded is not chopped or broken up in the roller mill, but rather crushed and broken up. This is done by several rotating knife rollers that mesh like cogwheels. For the chopped material, however, this means that it is comparatively coarse and therefore not suitable for mulching (ground cover), for example. The chopped material from a drum shredder therefore usually ends up on the compost pile.
In addition, shredding wet garden waste with a drum shredder can sometimes be problematic, as this can easily clog the drum mechanism. Particular care must be taken when processing longer branches and twigs, as these can sometimes whip through the air when fed into the machine. On the other hand, drum shredders are generally quieter than the blade shredders presented below.
Blade shredders
The second large class of garden shredders are the so-called blade shredders. The big advantage here is that the shredded material is particularly fine. At the heart of these appliances is a flywheel fitted with blades, which rotates very quickly around its own axis and therefore shreds the garden waste effectively. This is why blade shredders are primarily popular with ambitious hobby gardeners, as the shredded material is ideal as mulch for covering beds etc. due to its fineness. In this way, the soil does not dry out so quickly in summer, which would of course be fatal for fruit and vegetable yields.
Compared to drum shredders, blade shredders are louder, so that adequate hearing protection should be part of the operator's basic equipment, at least for longer periods of work. On the other hand, a blade shredder also gets the job done much faster, as the blades shred the material many times faster than the roller mill. Overall, the maintenance effort for a blade shredder is somewhat greater, as the blades need to be sharpened at regular intervals.
However, garden shredders have become established on the market that have taken the advantages of a 'simple' blade shredder and developed them further. These models not only have the aforementioned blades, but also a beater mechanism. Thanks to the extremely fast rotating beaters, even thicker branches are shredded effortlessly. Thanks to the perfect interaction with the specially hardened knife blades, the shredded material is impressively finer than with any other type of garden shredder. So if you are interested in pure shredding power and fast work, you should take a close look at these models.
Turbine shredder
Turbine shredders work on the principle of high-speed rotation. These machines consist of a turbine, similar to those in jet engines, which rotates at high speed. When the garden waste is fed into the shredder, it is torn apart by the powerful centrifugal force of the turbine and broken down into small pieces that can be composted or mulched.
Turbine shredders are very efficient and can process large quantities of garden waste in a short time. They also work much more quietly than roller or blade shredders. However, despite their high throughput, they do not come close to the performance of a blade shredder. They are also not suitable for overly hard or thick material.
A question of drive
Of course, the type of material shredding (blades/beaters vs. rollers) is not the only important factor in a garden shredder. The type of drive also has a considerable influence on the quality of the shredding results. Generally speaking, a distinction is made between electric shredders and petrol-powered garden shredders in this respect. And - how could it be otherwise - there are advantages and disadvantages here too, which you should bear in mind.
Shredders with electric drive
A garden shredder with an electric drive has the great advantage that they work comparatively quietly. In terms of design, these models are usually quite compact so that they can be easily stored in the shed once the work is done. In addition, the purchase costs are unlikely to make too big a dent in the household budget.
However, these advantages are offset by a whole series of disadvantages, which of course should not be concealed. For example, electrically powered garden shredders simply lack power. Plant waste, twigs and smaller branches can be shredded quite well, but beyond that it's quickly over. Then there is the matter of the power supply - sockets are notoriously rare in the garden. So you either have to drag the garden waste to the electric shredder or pull extension cables through the garden. Another major disadvantage is the working speed. If there's a bit more to shred, it can take quite a long time until you're finally finished.
Petrol-powered shredders
It is therefore not surprising that petrol shredders are increasingly being used, especially when there is a lot to do on a regular basis. In commercial use, for example in gardening and landscaping, there is practically no way around the petrol-powered solution.
The biggest advantage is probably the enormous shredding power - machines in the upper performance class do not even capitulate to branches approx. 10 cm thick. As a result, the shredded material is so fine that it is perfect for mulching or disappears into the organic waste garbage can to save space. You also benefit from the enormous mobility. As a petrol-powered garden shredder does not require a power connection, it can be moved freely (usually using large tires) through the garden or across the property. As well as being easy to use - these models pull the material in by themselves - petrol shredders are known for their speed of operation. No electric shredder can keep up with the speed at which they work. All this makes petrol-powered garden shredders the ideal tool for anyone who owns a large garden plot. Petrol-powered garden shredders are also the better choice for demanding challenges, such as the annual pruning of fruit trees.
Where there is so much light, there is naturally also a little shadow. Petrol-powered garden shredders usually have many times the power of an electric shredder, but in return you have to accept that a petrol shredder is louder than its electrically powered counterpart. Logically, the power has to come from somewhere. Earmuffs are a quick remedy here. Of course, you should also be considerate of your neighbors and not shred when it's quiet time. In addition, petrol-powered garden shredders are unfortunately somewhat more expensive to purchase than electric shredders. However, due to the fact that the petrol version shreds even huge amounts of plant waste effortlessly within a very short time, this effective garden tool is more than worth the money.
Garden shredder - maintenance and care tips
To ensure that you can enjoy your garden shredder for as long as possible and that the shredding results are always perfect, you should spend a little time checking and maintaining the shredder at regular intervals. It is always advisable to study the manufacturer's operating instructions carefully. This contains important information on maintenance and the intervals at which the individual steps should be carried out.
One of the most important points is regular basic cleaning (e.g. of the cutting mechanism) with a hand brush, as this keeps the moving parts going for longer. Before the garden shredder disappears into the garage for the winter, it is advisable to apply an oily maintenance spray to the blades etc. This prevents plant sap from penetrating the blades. This prevents plant juices from causing rust. The lubrication of the bearings should also be checked as often as possible. This saves a seized-up garden shredder and costly repairs.
Sharpening the individual blades is one of the most important tasks for blade shredders. This is the only way to guarantee the fine structure of the chopped material. Roller shredders are generally quite frugal when it comes to maintenance. However, the pressure plate should be readjusted from time to time if the work results become increasingly unsatisfactory.
All the maintenance work described here is quite easy to carry out, even for non-specialists. However, if you are not confident enough to re-sharpen or replace the blades yourself, you should contact a specialist garden tool company. They will help you quickly and reliably. Before buying a garden shredder, you should also take a close look at the dealer's other product range. What is particularly important here is the guaranteed long-term supply of spare parts. For example, a dealer who sells petrol-powered blade shredders should always have the right blades, V-belts, clutches, etc. on offer. This ensures that the spare parts are 100 percent compatible with your own garden shredder and that you will still be able to obtain important spare parts quickly and easily years from now.
How to work safely with your garden shredder
Of course, the important topic of work safety should not be forgotten in this guide. In principle, garden shredders have become increasingly safe in recent years. Nevertheless, there are a few points to bear in mind when working so that nothing can happen. The top priority is concentration - you must not be distracted by anything while shredding. Children, animals and people who are generally unfamiliar with the garden shredder should never be allowed near the shredder at any time.
It is essential to observe the following: Never put your hands in the garden shredder's intake when it is in operation! By law, the hoppers are designed in such a way that it is not possible to get into the cutting mechanism - but it is still better not to play with fire. If the garden shredder is clogged, it must be switched off before the fault is cleared. Only then can you carefully feel your way inside.
It is also very important that the garden shredder stands firmly and securely on level ground. This is the only way it can perform to its full potential and, above all, not fall over. For the best possible mobility, however, devices with large air-filled tires have proven their worth.
The right clothing is also part of occupational safety. Robust and hard-wearing work trousers and jackets as well as sturdy shoes are part of the basic equipment. Work gloves, earmuffs and safety goggles round things off nicely. This way, you are well protected against nasty thorns on branches, pieces of wood whirling around or sharp-edged branches.
The number of different models of garden shredders is almost as great as the number of cars on the market. It is therefore worth taking a closer look at what is on offer, especially when it comes to occupational safety. Particular attention should be paid to certain quality and safety certificates. For example, a safe garden shredder will have the well-known GS seal ("Tested Safety"). Garden shredders are particularly high-quality and technically mature if the manufacturer has had them tested and successfully certified on a voluntary basis by an independent testing institute (such as TÜV Rheinland).
Summary
This DENQBAR guide dealt with the question of what types of garden shredders exist and what their respective advantages and disadvantages are. The most important representatives, blade shredders and drum shredders, were then presented in more detail. A special subspecies of the blade shredder - a garden shredder equipped with both blades and rotating beaters - was also briefly discussed in this context. It was noted that blade shredders are essentially more powerful, but also louder than drum shredders. With regard to the structure of the shredded material, it was stated that a blade shredder shreds the source material much more finely than a drum shredder.
We also looked at the different drive types of garden shredders. A distinction is made here between petrol-powered garden shredders and electric shredders. The most important differences were identified as the noise level - an electric shredder is quieter than a petrol shredder - and the performance. The latter is much higher with a shredder with a petrol engine than with an electrically powered shredder, which means that the quality of the shredded material and the working speed of the petrol shredder are much more impressive. For example, a petrol-powered garden shredder shreds whole mountains of plant waste or fruit tree prunings at breakneck speed, while an electric shredder takes a much more leisurely approach.
For a long product life of the garden shredder, the important topic of maintenance was also addressed later in the guide. With these tips and advice, you will achieve the best shredding results over a long period of time. The final topic was working safety. In particular, the correct clothing and the correct handling of a garden shredder were highlighted. Important quality seals were also presented, which prospective buyers can use to recognize compliance with particularly high safety standards.
We hope that this guide has provided you with sufficient information on garden shredders - if you have any further questions or suggestions, we are always here to help and advise you!
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