Views: 0 Author: Site Editor Publish Time: 2026-10-23 Origin: Site
Surface finish of all contact surfaces on a food grade sigma mixer has significance other than aesthetic appeal. It determines the amount of product left in the chamber, aid to inspection, repeatability of clean down and amount of product lost on discharge. A polished contact surface is of benefit but a ‘dead’ area, an inaccessible seal or outlet which leaves a thick heel of product are not offset by a polished surface.
The right specification connects contact-material grade, surface condition, blade geometry, and cleaning method. For sticky fruit pulp, candy paste, bakery fillings, or other high-viscosity foods, the acceptance test should measure residue and cleanability as well as mixing uniformity. That is more useful than choosing a machine because its stainless-steel shell looks bright in a photograph.
· SS316 and mirror polishing are a material/surface choice not a full hygiene validation.
· The usable cleaning result of the apparatus is that of the whole chamber, blades, lid, seals, outlet and access points as one complete system.
· The surface has to be smooth to reduce adhesion but residue is a function of temperature, solids, sugar content and residence time of the formula.
· Check for product loss at the end of the screw and at the manual valve as well as on visible surfaces of the grinding chamber.
· Carries out a cleaning trial with original food or mock-up food that has same adhesion and viscosity.
Food paste is under compression in the paste contact areas of the chamber and blades. Surface scratches, poor welds, sharp transitions and unsmoothed corners in these areas can capture residue from previous batches. That residue can soften, burn or flake off in subsequent batches. A smooth surface does not solve all retention problems as some of these areas are designed as ‘pockets’ to be shielded from the paste.
Surface finish influences the inspection too. A polished stainless steel surface enables any discoloration, pits and any remaining product to be easily identified during a visual check. This is not only relevant during a short changeover but also during a full cleaning cycle. The question during an inspection is not only if the steel is shiny but also if all product contact surfaces can be easily seen by the operator and reached after the discharge and the cleaning of the equipment. When selecting equipment from the Karvil Machinery engineering range the complete contact surface has to be compared.
Keep these checks together:
· welds and internal transitions inside the chamber;
· Blade edges, blade roots and area near end plates.
· the lid, viewing window, vacuum connection and gasket groove;
· Screw outlet, ball valve and first part of downstream piping.
· All surfaces, especially shaft seals, not washed as part of normal wash down.
The finish is part of the food-contact surface and a smooth surface can form a thin film which is hard to see if it drizzles down to a low point and does not run off.
The Food Grade Sigma Z Blade Mixer offers contact surfaces of SS316 mirror-polished. In terms of the specifications for this mixer, the product page lists a 500 L full capacity / 350 L working capacity Sigma Z Blender fitted with double sigma blades. The blender is fitted with electric heating and is fitted with screw discharge which is completed with a DN125 manual ball valve.
When a formula, cleaning solution, amount of salt in a solution, etc. demands greater corrosion protection than normal processing equipment then SS316 could be the alternative to select. Material-compatibility is to be checked for the selected material. Ask for the material certificate, surfaces to be covered by the specified material and surface finish for welds and repaired areas. Stainless steel frames do not necessarily mean all internal parts are made of the same material.
Even a food-grade mixer with a highly polished mixing chamber can fail to remove all of the product from it if the blade clearance, mixing pattern or the outlet geometry are not suitable for the type of paste being made. The two Z blades in this example are designed to fold and compress the material being mixed. This action should cause the material to be returned to the mixing area rather than being turned into a ring at the side of the mixer and persisting there.
This food-grade model has 2 blade speeds 0-42 rpm and 0-34 rpm which are both inverter controlled. The variable speed allows the operator to set up separate stages for charging, kneading, heating and finishing. The highest speed is not necessarily the cleanest or safest setting. A high speed can cause a warm paste to be flung across the lid and seal of the mixer, whereas a low speed for the finishing stage could result in the center of the mixer not being worked enough.
When the discharge of the paste is a problem then the screw must move the final paste. The temperature and viscosity of this paste are known. The product can easily leave the chamber but than it blocks the outlet neck or even a manual ball valve. This has to be recorded during the test.
· batch temperature when discharge begins;
· screw speed and approximate discharge time;
· mass remaining in the chamber and outlet;
· time and method required to remove residue;
· condition of the gasket and valve after cleaning.
A short visual check of the tank can be misleading. A mixer may appear to be empty but there will still be a layer of material in the bottom of the tank, particularly in the low point and discharge area.
Electric heating of 18 kW and temperature of up to 120°C is listed for the food-grade page. While heating the paste can decrease its viscosity and make it easier to move through the screw, sugars, proteins and starch-rich residues can, however, bake onto surfaces that are exposed for too long. Thus, the cleaning instructions must specify an appropriate hold time and discharge temperature. In addition, it must be clarified whether a warm rinse or a separate cleaning step is allowed.
The useful trade-off is straightforward:
Do not make one setting your ‘golden rule’. Use the most difficult representative product in your cleaning validation trials, especially if your factory is making a change between fruit-based, confectionery, bakery and pharmaceutical-style pastes.
Process choice | Possible benefit | Main risk to check |
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Higher product temperature | Lower viscosity and easier discharge | Surface-baked residue, color change, or ingredient degradation |
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Higher blade speed | Faster folding for some pastes | Splashing, air incorporation, and product spread into seals |
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Lower filling level | More free space for blade movement | Slechte verbinding tussen het materiaal en de actieve bladzone. |
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Stronger cleaning action | Shorter residue-removal time | Gasket wear, surface damage, or chemical incompatibility |
|
Request a marked drawing showing all product-contact parts and their material. Check if all cover parts, blades, end plates, screw, valve, sight glass and gaskets are listed. A list of material for the chamber only is not sufficient for food processing.
1. After a representative batch has been processed, weigh or estimate the residue left in the processing chamber and the discharge path separately. Record the method used to arrive at the figures as a chamber that looks and feels clean to touch may have a thick film of solid left on it. Repeat this test after the proposed cleaning cycle has been completed and look for any problem areas by opening the lid.
Run two different formulas – i.e. different colors, different fat content, or different adhesion. Process the first one normally and then look for carryover in the second. Inspect the blade roots, outlet, valve, gasket groove and any low points that are not covered by material in normal processing.
More information on applications using Karvil Machinery in food and other high viscosity applications can be found on our Karvil Machinery's application resources. The site also contains information on sanitary mixing design using sanitary planetary mixers for pharmaceutical homogenization. The connected issues of access, contact surfaces and cleaning are addressed. Information on equipment considered by the company with respect to food-contact material compliance and FCM-related requirements can be found on the site. Please note that the exact scope of the certificate and the requirements for the destination market need to be confirmed from the purchase documentation.
No. Polishing will reduce retention points and make visual inspection easier, but hygiene is also affected by the welds, clearance, seals, drainage, access, cleaning agent and validation with the real product.
As the paste cools it may thicken. Also, a dead zone around the valve and outlet neck could cause problems. Check the discharge temperature, screw speed, outlet design, valve design and the amount of residue left after the batch.
Request the material grade for each product-contact part, surface-finish requirements, weld and repair records where applicable, gasket material, and certificates relevant to the intended food-contact regulation and destination market.
