Particle Uniformity with roller mills

In the current scenario, wholesale dry solid processors urge more processing from their machinery. Some processors that use the equipment for decreasing size have particular requirements such as product features that should be improved, improved process efficiency, and less usage of energy. Two Roller equipment can provide the solution to all these demands for various series of pharmaceuticals, chemicals, minerals, food, and other different products. Mills are suitable for minimizing materials that are fragile or breakable, which is the material that does not flatten but will break under compression, In a process when a consistently sized particle is required with more minor fines. 

Think of a coffee grinder machine in a process where the primary objective is to achieve maximum uniform particles for more excellent management of finished particle characteristics as in a large solid size reducing applications. In the united states, coffee beans are crushed and processed to attain the maximum particle yield, which is between 1170 and 590 microns, with lesser fines (particles that are under 417 microns). In contrast, some beans are processed finer, relying on the concluding use. For example, coffee makers process coffee beans to 1170 microns for utilizing, 300 microns for espresso, and 100 microns for Turkish coffee. After the grinding stage, the coffee is directed to the packaging without being organized. 

This well-structured procedure requires accurate grinding consistency. If the grinding creates variances in the particle size of the coffee or fines, then the coffee is over-extracted at the preparing step. This over-extraction step maximizes the bitterness of the coffee, which is something that all coffee manufacturers want to reduce. Many alternative size reduction strategies do not allow you to skip the categorizing stage.

Most applications require ground particles to be categorized for the final particles to meet tight size constraints. Furthermore, the fines eliminated during classification cost the producer money and energy because they must be discarded, reconditioned, or sold in a secondary market. The roller mill reduces such costs by precisely reducing input materials with an average particle size of up to 34 inches to a uniform average size of 100 to 2,000 microns.

Roller Mill Components And Operation

A roller mill comprises counter-rotating rolls of one to four pairs that are attached in a stiff frame horizontally, holding a feeding device placed on the top roll pair. Each pair has one roll that is placed in a fixed position, while others are allowed to move nearer or far from the fixed roll to accommodate the roll’s space, which is also called the roll gap. The size of the roll gap is based on the reduction of the desired particle size.

How Does The Mill Work?

In this process, the gravity-feeds material at a constant rate between the gap of the top pair of rolls. The feed material goes in the nip point where the opening between the rolls is the smallest. It is then crumbled into small particles as counter rolls rotate. If the mill has more than one roll pair, it will first crush it into smaller parts and then falls into the other nip point for further processing.

How The Mill Achieves Uniform Particle Size?

In order to attain a consistent particle size output with lesser fines, the roller mill, for your application, should contain a suitable roll surface, roll speed ratio, and roll gap.

Roll Surface

The roll surface is relatively crump as compared to being smooth to accomplish a reduction in adequate size. There are many corrugations in the variety available that is matchable to the hardness of the material and desired particle size output. Rolls, for example, can have longitudinal corrugations that run along the length of the roll or radial corrugations that run around the perimeter of the roll. Each corrugation can have several flutes (minor grooves) with varying sizes and profiles. To find out which corrugation is better for the application, the manufacturer will usually take roller mills tests in the testing facility for your material with different styles of roll corrugation and according to the circumstance similar to your operational environment.

Roll Speed Ratio

The rolls in each pair in most applications counter-rotate at various speeds. An HTD drive belt offers the motor powers both rolls and the speed discrepancy. Shear is applied to the material when it goes through the nip point when the rolls are operated at different speeds. The roll speed ratio is the difference in roll speeds between each pair (or roll speed differential). The roll speed ratio is 2:1 (1,000/500) if one roll rotates at 1,000 rpm and the other at 500 rpm. Less friable particles require more shear and a higher roll speed ratio. 

Running the rolls at the optimal roll speed ratio will produce the optimum shearing effect when the material goes through the rolls; the crushed particles will receive more tearing when the shear is much higher. As a consequence, the ratio of the roll speed has a more significant effect on the finished particle size supply, which relies on the friability of material and roll surface, and other characteristics.

Roll Gap

Proper controls of the roll gap are vital for achieving the desired particle size. This controller has two main components, i.e., roll alignment and the roll gap size. The mill operator can control size by narrowing or widening the roll gap. In most roller mills, the roller gap can be adjusted automatically through a PLC, programmed to match the specs of any product. This makes the gap adjustment process to be central seconds. It also allows faster changeovers between different grind settings and eliminates the need to shut down continuous operations. The rolls in pairs should be precisely the same as the roll length to achieve uniform size reduction. Testing the mill at the manufacturer's facility can help determine the ideal roll gap according to your size reduction requirements.

Growing Markets For Uniformly Reduced Particles

The two-roller machinery offers the distribution of a particle size ranging from 50 to 100 percent fewer fines than distributions formed by further attrition milling devices. This implies that no step of classifying is needed after roller mill reduction, and the mill makes less wastage in fines, minimizing discard requirements, reprocessing, or selling the wastage.